I can stiffen you can stiffen he can stiffen we can stiffen you can stiffen they can stiffen
V-ing form
I can be stiffening you can be stiffening he can be stiffening we can be stiffening you can be stiffening they can be stiffening
Perfect
I can have stiffened you can have stiffened he can have stiffened we can have stiffened you can have stiffened they can have stiffened
V-ing perfect
I can have been stiffening you can have been stiffening he can have been stiffening we can have been stiffening you can have been stiffening they can have been stiffening
Negation
Simple form
I can't stiffen you can't stiffen he can't stiffen we can't stiffen you can't stiffen they can't stiffen
V-ing form
I can't be stiffening you can't be stiffening he can't be stiffening we can't be stiffening you can't be stiffening they can't be stiffening
Perfect
I can't have stiffened you can't have stiffened he can't have stiffened we can't have stiffened you can't have stiffened they can't have stiffened
V-ing perfect
I can't have been stiffening you can't have been stiffening he can't have been stiffening we can't have been stiffening you can't have been stiffening they can't have been stiffening
Interrogative form
Simple form
can I stiffen? can you stiffen? can he stiffen? can we stiffen? can you stiffen? can they stiffen?
V-ing form
can I be stiffening? can you be stiffening? can he be stiffening? can we be stiffening? can you be stiffening? can they be stiffening?
Perfect
can I have stiffened? can you have stiffened? can he have stiffened? can we have stiffened? can you have stiffened? can they have stiffened?
V-ing perfect
can I have been stiffening? can you have been stiffening? can he have been stiffening? can we have been stiffening? can you have been stiffening? can they have been stiffening?
Interro-negative form
Simple form
can't I stiffen? can't you stiffen? can't he stiffen? can't we stiffen? can't you stiffen? can't they stiffen?
V-ing form
can't I be stiffening? can't you be stiffening? can't he be stiffening? can't we be stiffening? can't you be stiffening? can't they be stiffening?
Perfect
can't I have stiffened? can't you have stiffened? can't he have stiffened? can't we have stiffened? can't you have stiffened? can't they have stiffened?
V-ing perfect
can't I have been stiffening? can't you have been stiffening? can't he have been stiffening? can't we have been stiffening? can't you have been stiffening? can't they have been stiffening?